The coloring of keratinaceous fibers with oxidative dyes is usually carried out by the use of mixtures of couplers and primary intermediates (developers). These are chemical species which react with each other or with other chemical species to produce highly colored molecules of larger size. The efficiency of coloring by the couplers and developers is directly related to their functionality, i.e., the probability of interaction, and this is enhanced by the presence of multiple sites for coupling and/or other dye-forming reactions.
Several references deal with the production or use of pyrroles and N-aryl pyrroles.
J. S. Kiely and S. Huang in "The Synthesis of Methyl-1-Aryl-2-pyrrolecarboxylates", J. Hetrocyclic Chem., 24 (1987), pp. 1137-9 disclose the production of chemical intermediates whose structures generally resemble ##STR1## wherein R and R.sup.1 may be hydrogen, alkyl, phenyl, acetoxyphenyl, methoxy, or nitro moieties. These compounds are not discussed by the authors as useful in hair coloring.
The general chemistry of substituted pyrroles is described in R. C. Elderfield, ed., "Heterocyclic Compounds, Vol. 1", Chapter 6, John Wiley & Sons, Inc., New York, 1967 and in A. R. Katritzky, "Handbook of Heterocyclic Chemistry", Chapter 3.3, Pergamon Press, New York, 1985. Syntheses of N-aryl Pyrroles are detailed by N. Clauson-Kaas and F. Limborg, Acta Chem. Scand., 1952, 6, 551; and by S. Ram and R. E. Ehrenkaufer, Tet. Lett., 1984, 25, 3415. In Chemical Abstracts 47: 7482f, N. Elming and N. Clauson-Kaas disclose methods of making pyrroles from furans. Hair coloring is not mentioned.
Italian Patent No. 428,856 deals with the use of certain pyrroles in processes for coloring hair, where melanin-like materials are produced by the action of strong oxidants on the pyrroles.
U.S. Pat. No. 2,725,378 discloses pyrrole dyes having methine linkages. The dyes are made by condensing dimethylpyrroles with pyrrolealdehydes. The dyes are useful in photographic processing.
U.S. Pat. No. 4,560,769 refers to pyrroles of the formula: ##STR2## in which R.sub.1 and R.sub.2 may be H, C.sub.1-8 alkyl, C.sub.7-12 alkylaryl, C.sub.7-12 aralkyl or phenyl groups. The pyrroles are produced by reacting ammonia or R.sup.1 -NH.sub.2 with an R.sub.2 -substituted 1,4-dihydroxy-2-butene.
U.S. Pat. No. 4,567,272 teaches couplers for human hair dyeing among which are dyes of the formula: ##STR3## wherein X is H, C.sub.1-3 alkoxy or N(R.sup.1).sub.2. R.sub.1 and R.sub.2 are H or CH.sub.3 and n=0-3.
The disclosures of the publications discussed herein are hereby incorporated by reference, unless otherwise indicated.